usb: phy: rcar-gen2-usb: always use 'dev' variable in probe() method

The probe() method has the 'dev' local variable declared and used but strangely
not in all cases where it should be...

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>